Abstract: In order to study the mechanical behavior of lap-spliced carbon fiber reinforced polymer (CFRP)-steel composite bars (referred to as "composite bars") in coral sea-sand seawater concrete (CSSC) and determine the splice length of composite bars reasonably, tensile tests were conducted on 27 sets of 81 lap-spliced specimens and test variables included the composite bar diameter, splice length, cover thickness, concrete strength, clear space between the lap-spliced bars, stirrup ratio, concrete type, and reinforcement type. The influence of various test variables on the behavior of lap-spliced composite bars in CSSC was obtained. The results indicate that pull-out failure accompanied by concrete splitting is found for specimens with a splice length less than 17 times the diameter of the composite bar (d_c), while tensile fracture failure is found for specimens with a splice length greater than 17d_c. After the specimen undergoing pull-out failure, severe shear damage is formed on the surface of the composite bars. When the splice length is less than 14d_c, the splice strength of the specimen is about 7.2 MPa. When the splice length is greater than 14d_c, the splice strength of the specimen gradually decreases with the increase of the splice length. After the cover thickness is greater than 4d_c or the axial compressive strength of CSSC is greater than 30 MPa, the change in the splice strength of the specimen can be basically ignored. Increasing the stirrup ratio gradually increases the splice strength and significantly reduces the width of the splitting crack. Compared with the lap-spliced specimens of steel bars, the decrease in splice strength of the lap-spliced specimens of composite bars exceeds 25%. Based on the experimental results, the equations for calculating the splice strength and splice length of composite bars in CSSC were established, and the calculation results are consistent with the experimental results. Then, referring to the "Code for Design of Concrete Structures", the equation for calculating the splice length was simplified.